Drug Allergy – Diagnosis and Treatment
Diagnosis
Testing the Skin for Reactions
In many cases, skin assessments help identify if someone’s immune system reacts to a certain medication.
An allergist or nurse applies a small bit of the suspected drug to the skin using a fine needle, a shallow injection, or a patch placed on the surface.
A person may notice a red bump that feels itchy and is elevated—this is often a sign of an allergic response. When this happens, the healthcare professional records it as a possible sign of a drug allergy.
If no rash, hives, or irritation appear, this negative result can be helpful, but it does not always rule out the chance of being allergic, as some reactions may still occur with future exposures.
Symptoms monitored during these tests usually include:
| Symptom | Description |
|---|---|
| Rash | Red patches or spots on the skin |
| Hives (Urticaria) | Raised, itchy welts |
| Swelling | Enlargement of the skin or face |
| Itching | Persistent urge to scratch |
Skin testing is especially important for penicillin allergies and other common medication allergies.
Checking the Blood for Signs of Allergy
Doctors may order blood analysis when they suspect an allergic reaction, especially if the symptoms are not limited to the skin.
Blood tests look for markers that show if the immune system is involved, including IgE-mediated reactions, which are linked to type I hypersensitivity. These tests are not as widely available or researched for drug allergies as skin tests.
Sometimes, doctors choose blood tests when skin testing might be risky due to the chance of a severe reaction, like trouble breathing, wheezing, angioedema, or dizziness.
Blood results might help rule out other reasons for the symptoms, such as predictable reactions or drug hypersensitivity not linked to the immune system.
Understanding What the Tests Show
After the health professional reviews all symptoms, physical findings, and test results, he or she reaches a conclusion about the reaction:
- Confirmed Allergy: Evidence shows an allergy is present.
- No Allergy: Tests and symptoms do not support an allergy.
- Uncertain Allergy: There is not enough information for a definite answer.
For example, if a penicillin allergy is confirmed, doctors choose alternative treatments. If a drug allergy is ruled out, doctors may safely consider previously avoided drugs again.
Patients and doctors should communicate clearly about symptoms such as rashes, itching, swelling, or more serious reactions to ensure proper care for current and future medication use.
Treatment
Handling Ongoing Symptoms
When someone develops a drug allergy, the first step is to stop using the medicine believed to be the cause. Removing the drug from the person’s routine often helps symptoms get better.
If more help is needed, doctors give antihistamines such as diphenhydramine. These medications block certain immune chemicals that cause symptoms like itching, rash, or hives.
For more serious reactions, healthcare providers might use corticosteroids to help calm the body’s response.
If a person has signs of a severe allergic reaction, known as anaphylaxis—like trouble breathing or very low blood pressure—an epinephrine injection is needed right away. Emergency care may support breathing and keep blood pressure at safe levels.
Common Medicines for Treating Allergic Reactions
| Type | Used For |
|---|---|
| Antihistamines | Rash, hives, itching |
| Corticosteroids | Swelling, more severe symptoms |
| Epinephrine | Anaphylaxis (life-threatening reactions) |
What Happens If the Medicine is Still Needed?
Sometimes, people with drug allergies may really need a medicine, like certain antibiotics, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), chemotherapy drugs, or monoclonal antibodies.
If so, doctors try to find a safe way to give the drug, but only under careful observation. This usually happens when there are no other good treatment options or when the allergic reaction in the past was not very severe.
Any attempt to take the medicine again is closely watched by health professionals, who are ready to act quickly if an adverse drug reaction happens.
Step-by-Step Medicine Testing
If a doctor is not sure the person is truly allergic, they might recommend a “graded challenge” (also called a drug provocation test).
This involves giving the patient tiny doses of the medicine and slowly increasing the amount over a few steps. Usually, this test has two to five steps.
If the person does not have any side effects at the full dose, they may be able to use the medicine in the future. If symptoms appear during the test, doctors stop it right away.
Benefits of a Graded Approach:
- Confirms if an allergy is real.
- Limits the chance of a severe reaction.
- Helps pick the best treatment.
Step-by-Step Desensitization
If a drug allergy is confirmed but there’s no other medicine that can be used, doctors may try a method called drug desensitization. This process starts with a very small dose of the medicine.
Every 15 to 30 minutes, the dose is slowly made larger. This continues for several hours or days until the body becomes less likely to have an allergic reaction.
Once the full dose is reached with no serious symptoms, the patient can keep taking the medicine, but it must be taken daily. If the medicine is stopped even for a short time, the allergy might return and desensitization may need to be repeated.
Key Points About Desensitization:
- Always done in a hospital or clinic (never at home).
- Staff are ready with treatments in case of a severe reaction.
- Mostly used for drugs like penicillin, certain antibiotics, chemotherapy drugs, aspirin, and monoclonal antibodies.
Getting Ready for Your Visit
When you plan to see an allergist, preparing in advance can make the appointment more useful. Make a list of all the symptoms you have noticed, even those that seem minor or unrelated.
Write down when each symptom started and how long it lasted to help the healthcare team connect symptoms to possible triggers.
Key details to prepare:
- A list of all medicines you take, including both prescription and nonprescription drugs.
- Herbal products, vitamins, and supplements, along with the times you take them.
- Any changes in dosage or new medications you have recently started.
- Information about stopping or starting any regular medications.
Note if you tried anything to relieve symptoms and whether it worked. Bring photos of physical reactions such as rashes or swelling, especially if the symptoms have gone away by the appointment time.
Risk factors to note include:
- Previous allergic reactions to medications.
- Family history of drug allergies.
- Personal history of other allergies, such as to foods or pollen.
